Extruder apparatus and process for compounding thermoplastic resin and fibres

Abstract

Multiple extruder apparatus for compounding thermoplastic resin and reinforcing fibers incorporates a resin extruder in which thermoplastic resin pellets are melted and a compounding extruder in which the molten thermoplastic resin is mixed in intimate contact with long reinforcing fibers of at least one inch in length. The melted thermoplastic resin is introduced into the compounding extruder at a point downstream of the inlet point for the reinforcing fibers, so that the fibers are mechanically worked and heated before coming into contact with heated, molten thermoplastic resin. The extrudate from the compounding extruder consists of a homogeneous, molten mass of thermoplastic resin having discrete lengths of fibers randomly dispersed therein.

What is claimed is: 
     
       1. Apparatus for compounding reinforcing fibers with a thermoplastic resin comprising: a source of supply of thermoplastic resin pellets;   a resin extruder having an inlet for receiving thermoplastic resin pellets from said source of supply, an outlet, an elongated, rotatable extruding screw extending between said inlet and said outlet;   pellet handling means for conveying thermoplastic resin pellets from said source of supply thereof into said resin extruder inlet, whereby thermoplastic resin pellets are mechanically pumped by said resin extruder screw from said inlet to said outlet and are thereby heated and melted;   a compounding extruder comprising a single, continuous, straight barrel and an elongated, rotatable, power screw extending continuously therein between an inlet end and a discharge end of said barrel, said barrel having first and second inlet ports on said inlet end communicating with said power screw, said second inlet port being continuously connected in fluid flow relation to said outlet of said resin extruder for receiving molten thermoplastic resin therefrom at a location along said elongated power screw downstream from said first inlet port, and between said first inlet port and said discharge end of said compounding extruder barrel, and said power screw having substantially continuous thread means of generally helical configuration;   a converging, flow restricting passage at said discharge end of said barrel of substantially less diameter than the diameter of said barrel;   a source of supply of discrete, predetermined lengths of reinforcing fibers connected to said first inlet port of said compounding extruder, and means for feeding said fibers into said first inlet port, whereby the fibers are heated and mechanically worked by said power screw of said compounding extruder before coming into mixing contact with molten, thermoplastic resin, and the fibers are continuously confined under pressure within said screw barrel by said thread means and advanced by said thread means of said power screw as a continuous mat past said second inlet port for thorough initial wetting by molten thermoplastic resin, and said fibers and said thermoplastic resin intermix in said power screw to form a homogeneous molten mass of thermoplastic resin having discrete, discontinuous lengths of reinforcing fibers randomly and homogeneously dispersed therein.   
     
     
       2. Apparatus as defined in claim 1 wherein: said thermoplastic resin pellet handling means comprises weighing and conveying apparatus positioned to receive thermoplastic resin pellets from said source of supply thereof and to feed thermoplastic resin pellets into said resin extruder inlet at a predetermined weight rate; and   said means for feeding said fibers into said first inlet port of said compounding extruder comprises weighing apparatus on which fibers are received and weighed and conveying apparatus positioned adjacent to said weighing apparatus to feed discrete lengths of reinforcing fibers into said first inlet port of said compounding extruder at a predetermined weight rate.   
     
     
       3. Apparatus as defined in claim 2, wherein: said weighing apparatus for said thermoplastic resin pellets and said weighing apparatus for said reinforcing fibers each comprises a loss-in-weight feed scale.   
     
     
       4. Apparatus as defined in claim 2 wherein: said source of supply of reinforcing fibers comprises continuous lengths of fibers on supply means positioned on a feed scale to serve as a fiber source, and said means for feeding said fibers comprises a pair of feed rollers rotating at a predetermined speed and positioned adjacent to said supply means, and a movable cut-off knife, and a feeder hopper positioned in fiber-receiving relation to said feed rollers and having an outlet connected to said first inlet port of said compounding extruder, whereby said feed rollers pull continuous lengths of fibers from said supply means and said cut-off knife cuts the fibers to said predetermined lengths, with the cut fibers being received in said feeder hopper, from which they are conveyed into said first inlet port of said compounding extruder.   
     
     
       5. Apparatus as defined in claim 4, wherein: a computer is connected is signal-receiving relation with said weighing apparatus for said fibers and in signal generating and sending relation with said feed rollers, said computer being programmed to provide a predetermined input feed rate of fibers, and said computer providing signals to said feed rollers to adjust said predetermined speed thereof in response to signals received by said computer from said fiber-weighing apparatus indicating the weight of fibers being fed from said source of supply.   
     
     
       6. Apparatus as defined in claim 2 wherein: said pellet-handling means further comprises a dryer through which thermoplastic resin pellets are conveyed for drying prior to being introduced into said inlet of said resin extruder.   
     
     
       7. Apparatus as defined in claim 2 wherein: said weighing and conveying apparatus for said thermoplastic resin pellets comprises a conveyor supported on a feed scale for conveying thermoplastic resin pellets to said inlet of said resin extruder at a predetermined weight rate.   
     
     
       8. Apparatus as defined in claim 1 wherein: a preforming device for forming the extrudate from said compounding extruder into a predetermined size, weight and shape of preformed mass is directly positioned at said discharge end of said compounding extruder.   
     
     
       9. Apparatus as defined in claim 8 wherein: said preforming device comprises a pair of rollers having an input side and an output side and defining a nip, said input side being a fluid-flow communication with said discharge end of said compounding extruder to receive extrudate therefrom, whereby the extrudate is formed as a sheet-shaped preform by passing through said nip between said rollers, and further including a cut-off means adjacent the output side of said pair of rollers to cut sheet preforms into desired lengths.   
     
     
       10. Apparatus as defined in claim 1 wherein: said screw of said resin extruder and said power screw of said compounding extruder are of different sizes and have different volume flow capacities.   
     
     
       11. Apparatus as defined in claim 1 wherein: separate, power-drive means are independently, drivingly connected to said screw of said resin extruder and to said power screw of said compounding extruder for driving said screw and said power screw at predetermined rotational speeds, whereby said screw of said resin extruder and said power screw of said compounding extruder can be independently driven and controlled.   
     
     
       12. Apparatus as defined in claim 1 wherein: said second inlet port is at a location on said barrel such that at least one-half the overall length of said power screw extends between said second inlet port and said discharge end of said barrel.   
     
     
       13. Apparatus as defined in claim 8 wherein: said preforming device comprises means for forming said extrudate from said compounding extruder into an elongated billet, said preforming device having a discharge end through which a measured volume of an elongated billet comprising a homogeneous mixture of thermoplastic resin and reinforcing fibers is discharged;   the apparatus further comprising a cut-off knife positioned for movement across said discharge end of said preforming device to cut said elongated billers to predetermined lengths suitable for reception in a compression molding machine; and   a compression molding machine positioned adjacent to said preforming device; and   shuttle plate means positioned immediately adjacent to said discharge end of said preforming device and reversibly movable between said preforming device and said compression molding machine to receive said elongated billets one at a time from said discharge end of said preforming device and deliver them to said compression molding machine.